A “link” is a mechanical device that is used for connecting the ball segments of a flexible mandrel that is used in the rotary-draw tube-bending process. As seen in FIG. 1, a typical mandrel assembly 100 includes a mandrel body 101, a nose 103, and a plurality of balls 105 and links 107, 108, 109. The assembly is inserted inside a tube in order to support its circumference or perimeter as the tube is bent using a rotary-draw tube-bending machine. Those skilled in the art will recognize that FIG. 1 illustrates a mandrel for a round tube; however, the present invention is not limited to that shape.
Further, a ball 105 fits over each link 107, 108, 109 and acts as a joint for allowing the ball to move and flex along with the tube as it is drawn over the mandrel and bent into an arc around a rotating die. Although many types of links are known in the art, the universally flexible link is best known for allowing the mandrel balls to flex in any plane during the tube bending process. As with most links, over time each ball will wear at a different rate and must be replaced to prevent the balls from developing an undesired play or slop. If not replaced, this slop will prevent tubes from maintaining a consistent circumference or perimeter throughout the arc of the bend.
Universally flexible links come in two main configurations or styles, namely the “poppet” style and the “split link” style. The poppet style link is a single piece construction where the socketed end of one link is pressed over the head of another. The socketed end, known as the barrel, is longitudinally slotted so that it opens and closes as it is pressed over the head of the other link. The poppet style link is generally less expensive to manufacture than the split link style, but it can be more difficult to assemble into a mandrel.
In contrast, a split link includes a system where the link is formed in two or more pieces that are joined together. As seen in U.S. Pat. No. 3,190,106 to Spates, which is herein incorporated by reference, Spates FIGS. 1-2 illustrate a tube bending mandrel using balls connected with links. Each link member is formed in longitudinal halves that are connected along a common line of division. In order to prevent each of the link halves from sliding against one another, the head of each half is keyed to the other into a fixed position for preventing such longitudinal movement. Other types of multi-piece designs provide a serpentine or zigzag type of joint along the common line of division for preventing movement. Still others are configured so that the head of the link is segmented into various pieces for joining the link halves to one another.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.